Recently, hybrid vehicles are widely attracting attention as environment-friendly vehicles. The hybrid vehicles have partly been brought into practical use.
The hybrid vehicle is powered by a DC (Direct Current) power source, an inverter, and a motor driven by the inverter, in addition to a conventional engine. Specifically, while it is powered by driving the engine, it is also powered by converting DC voltage from the DC power source to AC (Alternating Current) voltage by the inverter and rotating the motor by the converted AC voltage.
Among such hybrid vehicles, a hybrid vehicle equipped with two AC motors M1 and M2 as shown in FIG. 5 can be found. AC motor M1 is a motor for producing torque for driving the driving wheels of the hybrid vehicle. AC motor M2 is a motor connected to the engine of the hybrid vehicle and generates electric power by the rotation of the engine at regenerative braking of the hybrid vehicle.
Inverter 330 receives a predetermined DC voltage from a positive bus L1 and a negative bus L2, and converts the received predetermined DC voltage to AC voltage based on a control signal from a control apparatus (not shown), and drives AC motor M1. Inverter 340 converts AC voltage generated by AC motor M2 to DC voltage based on a control signal from a control apparatus (not shown), and supplies the converted DC voltage to positive bus L1 and negative bus L2. DC voltage supplied to positive bus L1 and negative bus L2 is supplied to inverter 330, or it may be used to charge a DC power source (not shown).
In a hybrid vehicle equipped with such two AC motors M1 and M2, when one of two AC motors M1 and M2 is stopped due to failure or the like, it is a critical issue how to control the other AC motor for the safe driving of the hybrid vehicle.
From such a viewpoint, when one of two AC motors M1 and M2 mounted on a hybrid vehicle is stopped due to failure or the like, generally the other AC motor is stopped. Specifically, when one of the AC motors stops, the other AC motor stops as well.
However, among hybrid vehicles or electric vehicles, some hybrid vehicles are each equipped with a system for boosting DC voltage from DC power source and supplying the boosted DC voltage to two inverters driving two AC motors. In the technique disclosed in Japanese Patent Laying-Open No. 2000-166012, there exist a problem in such a system with a voltage converter for boosting DC voltage, that when one of the AC motors stops, the other AC motor cannot practically be controlled.